The answer is A. <span>effective length of the tube
In wind instrument, the effective length is not the actual length of the instrument but only the length that the finger holes manage to cover.
The more holes it managed to cover, the higher frequency of vibration it might able to produce, which lead to higher pitch of the instrument.</span>
There are no true tropic climates
It would be the vital capacity
Rice Plants need to stand in a lot of water for growth. The Borders (bunds) of a rice field have to be Strong to hold the Water. The Farmer Planted Grass Plants on the Borders because, Grass has Fibrous roots which bind the soil of the bund and hold it together.
<u>Explanation</u> : The Answer itself Explains us well about why the farmer planted those grass plants (i.e.) to increase the strength of the soil. We know that Unity and Teamwork are Strong Words. The Soil and Fibrous Roots show us How Strong those Words are!
